Vast amounts of research in the past have shown that the evoked oculomotor vectors reflect the process of visuomotor coordinate transformation. Some recent studies have shown that non-oculomotor variables, such as vestibule and/or neck proprioception, can alter the oculomotor coordinates. Our preliminary studies further indicate that the directions of the neurally evoked saccadic vectors in the frontal eye field (FEF) are shifted in the compensatory direction with respect to changes in static vertical head position. These findings together suggest that the vestibule and/or neck inputs may be critical in updating the visuomotor coordinate frames even if the head is not moving. Based on these findings, we hypothesize that the otoliths, the inner ear organs dedicated to the detection of static head position with respect to gravity, may provide critical inputs to the frontal cortex to help shape the oculomotor coordinates. Alternatively, the neck proprioceptive inputs, which often vary together with the vestibular signals, may be important. To determine whether our findings are contributed solely by vestibular inputs (vestibule hypothesis), neck proprioceptive inputs (neck hypothesis), or both, we have developed a novel approach which permits dissociation of vestibular and neck influences based on independent control of the pertinent movement variables, e.g. initial eye position (IEP), initial head position (IHP), and initial neck position (INP), in head-unrestrained animals. The predictions of the working hypotheses will be evaluated by systematic manipulation of these variables in the proposed experiments. Under Specific Aim 1, we will assess whether vestibular and/or neck proprioceptive inputs participate in the visuomotor coordinate processing (i.e. determining the directions of the stimulation-evoked saccades) in the FEF and supplementary eye field (SEF) of head-unrestrained monkeys. Under Specific Aim 2, we will determine if the vestibular and neck proprioceptive input updates the motor and/or visual coordinates of FEF and SEF neurons. These experiments are expected to bring insights into the understanding of cortical processing of spatial coordinates, and the findings will be important to further the understanding of the neural mechanisms of motor control in general.